1. Field of the Invention
The present general inventive concept relates to an inkjet printhead, and more particularly, to a piezoelectric inkjet printhead formed of two silicon substrates using a micro-fabrication technology and a method of manufacturing the piezoelectric inkjet printhead.
2. Description of the Related Art
Generally, inkjet printheads are devices for printing a color image on a printing medium by ejecting droplets of ink onto a desired region of the printing medium. Depending on the ink ejecting method, the inkjet printheads can be classified into two types: thermal inkjet printheads and piezoelectric inkjet printheads. The thermal inkjet printhead generates bubbles in ink to be ejected by using heat and ejects the ink utilizing an expansion of the bubbles, and the piezoelectric inkjet printhead ejects ink using pressure generated by deforming a piezoelectric material.
FIG. 1 is a view illustrating a general structure of a conventional piezoelectric inkjet printhead. Referring to FIG. 1, a manifold 2, a restrictor 3, a pressure chamber 4, and a nozzle 5 are formed in a flow channel plate 1 to form an ink flow channel. A piezoelectric actuator 6 is formed on a top area of the flow channel plate 1. The manifold 2 allows an inflow of ink from an ink tank (not illustrated), and the restrictor 3 is a passage through which the ink flows from the manifold 2 to the pressure chamber 4. The pressure chamber 4 contains ink to be ejected and is deformed by an operation of the piezoelectric actuator 6. Thus, pressure inside the pressure chamber 4 varies, causing the ink to flow into or out of the pressure chamber 4.
Conventionally, the flow channel plate 1 is formed by individually fabricating a silicon substrate and a plurality of thin metal or synthetic resin plates to form the ink channel portion and by stacking the thin plates. The piezoelectric actuator 6 is formed on the top area 1a of the flow channel plate 1 above the pressure chamber 4 and configured with a piezoelectric layer and an electrode stacked on the piezoelectric layer to apply a voltage to the piezoelectric layer. Therefore, a portion of the flow channel plate 1 forming an upper wall of the pressure chamber 4 functions as a vibrating plate 1a that is deformed by the piezoelectric actuator 6.
An operation of the conventional piezoelectric inkjet printhead will now be described. When the vibrating plate 1a is bent downward by the operation of the piezoelectric actuator 6, a volume of the pressure chamber 4 reduces, which increases the pressure inside the pressure chamber 4, causing the ink to flow from the pressure chamber 4 to an outside of the printhead through the nozzle 5. When the vibrating plate 1a returns to an original shape after being bent downward according to the operation of the piezoelectric actuator 6, the volume of the pressure chamber 4 increases, which reduces the pressure of the pressure chamber 4, causing the ink to flow from the manifold 2 into the pressure chamber 4 through the restrictor 3.
An example of a conventional piezoelectric inkjet printhead is disclosed in U.S. Pat. No. 5,856,837. The disclosed piezoelectric inkjet printhead is formed by stacking and bonding a number of thin plates. To manufacture the disclosed piezoelectric inkjet printhead, a number of metal plates and ceramic plates are individually fabricated using various methods, and then the plates are stacked and bonded together using an adhesive. However, since the conventional piezoelectric inkjet printhead is formed of a relatively large number of plates, the number of plate-aligning processes increases and thereby a number of aligning errors also increases. In this case, ink cannot flow smoothly through an ink flow channel formed in the printhead, thereby deteriorating an ink ejecting performance of the printhead. Particularly, since recent printheads have a highly integrated structure for high resolution printing, precise alignment becomes very important in manufacturing the printhead. Further, precise aligning may influence a price of the printhead.
In addition, since the plates of the printhead are formed of different materials using different methods, the manufacturing process of the printhead is complicated and it is difficult to bond the plates, thereby decreasing a manufacturing yield of the printhead. Further, since the plates of the printhead are formed of different materials, the alignment of the plates may be affected or the plates may be deformed according to a temperature change due to different thermal expansion characteristics of the plates, even though the plates are precisely aligned and bonded together in the manufacturing process.
FIG. 2 is a view illustrating another example of a conventional piezoelectric inkjet printhead disclosed in Korean Patent Laid-Open Publication No. 2003-0050477 (U.S. Patent Application Publication No. 2003-0112300).
The piezoelectric inkjet printhead illustrated in FIG. 2 has a stacked structure formed by stacking and bonding three silicon substrates 30, 40, and 50. An upper substrate 30 includes pressure chambers 32 formed in a bottom surface thereof to a predetermined depth and an ink inlet 31 formed through one side thereof to connect with an ink reservoir (not illustrated). The pressure chambers 32 are arranged in two lines along both sides of a manifold 41 formed in a middle substrate 40. Piezoelectric actuators 60 are formed on a top surface of the upper substrate 30 to apply driving forces to the pressure chambers 32 for ejecting ink. The middle substrate 40 includes the manifold 41 connected with the ink inlet 31 and a plurality of restrictors 42 formed on both sides of the manifold 41 to connect with the respective pressure chambers 32. The middle substrate 40 further includes dampers 43 formed therethrough in a vertical direction at positions corresponding to the pressure chambers 32 formed in the upper substrate 30. A lower substrate 50 includes nozzles 51 connected with the dampers 43. Each of the nozzles 51 includes an ink introducing portion 51a formed in an upper portion of the lower substrate 50, and an ink ejecting hole 51b formed in a lower portion of the lower substrate 50. The ink introducing portion 51a is formed into a reversed pyramid shape by anisotropic wet etching, and the ink ejecting hole 51b is formed into a circular shape having a uniform diameter by dry etching.
As described above, since the inkjet printhead of FIG. 2 is configured with three stacked silicon substrates 30, 40, and 50, the number of substrates is reduced when compared with the inkjet printhead disclosed in U.S. Pat. No. 5,856,837, and thus the manufacturing process of the inkjet printhead can be simply performed with less substrate-aligning errors when compared with the inkjet printhead disclosed in U.S. Pat. No. 5,856,837.
However, the inkjet printhead manufactured using the three substrates 30, 40, and 50 has low driving frequency and high manufacturing costs.
Further, when a number of ink introducing portions 51b are formed by wet etching as described above, it is difficult to keep the ink introducing portions 51b at a constant depth such that a length of the ink introducing portions 51b may deviate from a desired value. In this case, an ink ejecting performance through the ink introducing portions 51b may vary, that is, an ejecting speed and volume of ink droplets may vary.